Device and method for supporting harq

ABSTRACT

The present invention relates to HARQ, particularly for IEEE 802.11, i.e. Wi-Fi. The invention proposes a transmitting device for supporting such HARQ, in which the order of scrambling and encoding is changed compared to the conventional transmitter. Likewise the invention proposes a receiving device for supporting such HARQ, in which the order of descrambling and decoding is changed compared to the conventional receiver. In particular, the transmitting device is configured to encode at least one data unit using Forward Error Correction (FEC) coding, scramble the encoded data unit based on a scrambling seed, provide an indication of the scrambling seed that is separate from the scrambled and encoded data unit, and transmit the indication of the scrambling seed and then the scrambled and encoded data unit to a receiving device.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of International Application No.PCT/EP2018/078895, filed on Oct. 22, 2018, the disclosure of which ishereby incorporated by reference in its entirety.

TECHNICAL FIELD

The present invention relates to Hybrid Automatic Repeat Request (HARQ)in wireless communication technologies, particularly HARQ for IEEE802.11, i.e. HARQ for Wi-Fi. To this end, the invention proposes atransmitting device and a receiving device, respectively, bothconfigured to support such HARQ in Wi-Fi, and further proposescorresponding HARQ methods that are compatible with IEEE 802.11.

BACKGROUND

HARQ is a widely used method in wireless and cellular technologies,wherein past transmission and current retransmissions are combined, inorder to improve the decoding performance. All currently existing 802.11standards—i.e. a/b/g/n/ac/ax—do not support HARQ. In particular, incommunication systems according to these standards the coded data bitsundergo scrambling at the transmitter side, and the used scrambling seedis encoded with the data payload. This means that at the receiver side,the scrambling seed used for scrambling (and hence needed fordescrambling) can be known only after decoding, and thus only decodedbits can be descrambled. This means that Log Likelihood Ratios (LLR) atthe input to the receiver cannot be descrambled and cannot be combinedin a HARQ fashion.

Furthermore, 802.11 communication systems typically use an AggregatedMedium Access Control (MAC) Protocol Data Unit (A-MPDU), in whichmultiple MPDUs (i.e. data units) are aggregated to form a longtransmission (hence in effect reduced overhead), i.e. a single PhysicalProtocol Data Unit (PPDU). Since the physical layer (PHY) operates onthe entire PPDU, regardless of the MPDUs, the scrambling seed is encodedwith the first MPDU. If the first MPDU is decoded correctly, and at thesame time at least one MPDU fails decoding, the transmitter willretransmit the failed MPDU, and will attach an indication of the usedscrambling seed to the (now) first MPDU. This means that after theencoding, specifically Forward Error Correction (FEC) encoding, at thetransmitter side, the coded bits will be different from the previoustransmission, making combining at the receiver side effectivelyimpossible.

In all current versions of the 802.11 standard (a/g/n/ac/ax), thescrambler operates on information bits (provided by the MAC layer to thePHY) at the transmitter side before invoking the FEC operation(encoding)—be it either Binary Convolutional Coders (BCC) or Low DensityParity Check Code (LDPC). For example, FIG. 7 shows a block diagram foran 802.11n transmitter 700, whereas FIG. 2 shows a block diagram for an802.11ax transmitter 800. In both transmitters 700, 800 a scrambler 701,801 is provided before an FEC/BCC encoder 702, 802.

The scrambler 701, 801 is used to avoid long sequences of same repeatedbits (either many 0s or 1s) in the bit-stream, hence its output shouldbe at least pseudo-random. This helps taming the Peak to Average PowerRatio (PAPR), and also ensures that interfering transmissions from otherStations (STAs), i.e. transmitters 700, 800, —in the extreme case theyare synchronized—behave more like random noise.

The scrambling seed of the scrambler 701, 801 is thus randomly chosen,and typically changes between transmissions, so as to restrain the PAPRon average. Every data portion of the PPDU (including one or more dataunits) is typically prepended with a 16-bit SERVICE field, whichcontains 7 bits of scrambler initialization and 9 zero bits. The SERVICEfiled 900 is shown in FIG. 9. The SERVICE field 900 serves as anindication of the scrambling seed.

The SERVICE field 900 is then encoded together with the data portion.This means that when e.g. LDPC is used, (only) the first LDPC codewordcontains the SERVICE field. At the receiver side, directly after theprocess of data decoding starts, the first 7 bits at the output of thedecoder (respective to scrambler initialization) are used to configurethe descrambler.

The configuration of the scrambler 701, 801 (including SERVICE field900) and FEC e.g. in IEEE 802.11, as described above, has the followingdisadvantages:

-   -   The scrambling seed information (within the SERVICE field 900)        is included with the first MPDU, hence any retransmission of an        MPDU, which is not the first within a new transmission must        include the SERVICE field 900, thus changing the coded bits.    -   Since the descrambler is deployed after the FEC decoder (at the        receiver side), in order to make it compatible with HARQ, the        scrambling seed would have to be the same for every        (re)transmissions, in order to ensure that (possibly different        redundancy versions of) the same codeword are carried by both        the original transmission and the following (optional)        retransmissions.    -   The SERVICE field 900 undergoes the same coding and modulation        as the data payload, implying that an error in decoding the        scrambling seed leads to a failure of decoding the entire PPDU,        even if there are no errors anywhere within the PPDU's actual        payload.

SUMMARY

In view of the above-mentioned problems and disadvantages, embodimentsof the present invention aim to improve the current implementations. Anobjective is to make wireless communication technologies, particularlyIEEE 802.11, i.e. Wi-Fi, compatible with HARQ. Thereby, all(re)transmissions should use a (semi-)random scrambling seed (just likenon-HARQ retransmissions). Further, a robust scheme should be providedfor indicating the scrambling seed to the receiving side, in order toprotect the scrambling seed and thus to avoid (or at least make it muchless likely) that an error in decoding the indication of the scramblingseed leads to a failure of decoding an entire (aggregated) data unit.The scheme of the invention should further be compatible with thecurrent implementations.

The objective of the present invention is achieved by the solutionprovided in the enclosed independent claims. Advantageousimplementations of the present invention are further defined in thedependent claims.

In particular the present invention proposes a transmitting device thatperforms scrambling after FEC encoding, and a receiving device thatperforms descrambling before FEC decoding. Additionally, a scramblingseed indication is separated from the transmitted data units.

A first aspect of the invention provides a transmitting device for HARQ,the transmitting device being configured to: encode at least one dataunit using FEC coding, scramble the encoded data unit based on ascrambling seed, provide an indication of the scrambling seed that isseparate from the scrambled and encoded data unit, and transmit theindication of the scrambling seed and then the scrambled and encodeddata unit to a receiving device.

Accordingly, unlike in the current transmitter implementations, the FECis performed before scrambling, i.e. a FEC encoder may be arrangedbefore a scrambler in the transmitting device. In this way, combinationsof multiple transmissions become possible with a (e.g. random)scrambling seed that is changed each transmission. Further, byseparating the indication of the scrambling seed from the data unit(s),the indication can be provided in a more robust manner to the receivingdevice, thus reducing decoding errors. Separate means that theindication of the scrambling seed is either transmitted apart, from thedata unit(s), or is encoded and/or modulated differently than the dataunit(s).

Without the switching of the scrambling and FEC encoding, it would be inpractice impossible to descramble LLRs, and combine them at thereceiving device for multiple retransmissions. Furthermore, without theseparation of the indication of the scrambling seed from the dataunit(s) (data payload), every retransmission, where the first data unitis different from a previous transmission, would result in a differentsets of coded bits, which means that their LLRs could not be combined.

A data unit may be a MPDU. Multiple data units may be an A-MPDU, i.e. aPPDU.

In an implementation form of the first aspect, the transmitting deviceis configured to: encode and/or modulate the indication of thescrambling seed separately from the at least one data unit.

Thus, the scrambling seed can be encoded and/or modulated in a morerobust manner, e.g. with a stronger encoding or modulation scheme, inorder to reduce the risk of decoding errors. Thus, it is less likelythat decoding the entire data unit(s) fails, and less retransmission arenecessary.

In a further implementation form of the first aspect, the transmittingdevice is configured to: include the indication of the scrambling seedin a PHY preamble.

In a further implementation form of the first aspect, the transmittingdevice is configured to: include the indication of the scrambling seedin a Signal A (SIG-A) field or Signal B (SIG-B) field.

In a further implementation form of the first aspect, the transmittingdevice is configured to: define the indication of the scrambling seedbased on predetermined bits of one or more signaling fields.

The above implementation forms are easy, but efficient options toseparate the indication of the scrambling seed from the one or more dataunit(s).

In a further implementation form of the first aspect, the transmittingdevice is configured to: encode the indication of the scrambling seedusing a Binary Convolution Code (BCC).

Thus, the indication is encoded in a different manner than the dataunit, particularly more robust. The FEC encoding of the data unit(s) iscompatible with current implementations.

In a further implementation form of the first aspect, the transmittingdevice is configured to: encode the indication of the scrambling seedusing a block code.

Thus, the indication is encoded in a different manner than the dataunit, particularly simple and more robust. The FEC encoding of the dataunit(s) is compatible with current implementations.

In a further implementation form of the first aspect, the transmittingdevice is configured to: encode the indication of the scrambling seedusing a Hadamard code as a generator matrix.

In a further implementation form of the first aspect, the transmittingdevice is configured to: modulate the indication of the scrambling seedusing Binary Phase Shift Keying (BPSK).

Thus, a strong modulation is used for the indication, making it lessprone do errors.

A second aspect of the invention provides a receiving device forsupporting HARQ, the receiving device being configured to: receive froma transmitting device an indication of a scrambling seed and then atleast one scrambled and encoded data unit that is separate from theindication of the scrambling seed, descramble the scrambled and encodeddata unit based on the scrambling seed determined from the indication ofthe scrambling seed, and decode the encoded data unit using FECdecoding.

Accordingly, unlike in the current receiver implementations, the FECdecoding is performed after descrambling, i.e. a FEC decoder may bearranged after a descrambler. In this way, combination of multipletransmissions becomes possible with a changing (e.g. random) scramblingseed. Further, by receiving the indication of the scrambling seedseparately from the data unit, the indication can be decoded in a morerobust manner, thus reducing decoding errors.

In an implementation form of the second aspect, the receiving device isconfigured to: send to the transmitting device an Acknowledge (ACK)and/or a Not Acknowledge (NACK) message, regarding at least one dataunit that was correctly and/or incorrectly decoded, receive from thetransmitting device, if decoding of at least one data unit failed, afurther indication of a scrambling seed and then a scrambled and encodedretransmission of the failed data unit that is separate from the furtherindication of the scrambling seed, descramble the scrambled and encodedretransmission of the failed data unit based on a scrambling seeddetermined from the further indication of the scrambling seed, decodethe encoded retransmission of the failed data unit using FEC decoding,and soft combine the retransmission of the failed data unit with thepreviously received failed data unit.

Thus, the receiving device is configured to support and perform HARQ,particularly for Wi-Fi.

In a further implementation form of the second aspect, the receivingdevice is configured to: decode and/or demodulate a received indicationof a scrambling seed separately from a received scrambled and encodeddata unit.

In a further implementation form of the second aspect, the receivingdevice is configured to: derive an indication of a scrambling seed frompredetermined bits of one or more signaling fields received from thetransmitting device.

In a further implementation form of the second aspect, the receivingdevice is configured to: extract an indication of a scrambling seed froma PHY preamble, particularly from a SIG-A field or SIG-B field, receivedfrom the transmitting device.

With the above implementation forms, the advantages described for thecorresponding implementation forms of the transmitting device areachieved.

A third aspect of the invention provides a method for supporting HARQ,the method comprising: encoding at least one data unit using FEC coding,scrambling the encoded data unit based on a scrambling seed, providingan indication of the scrambling seed that is separate from the scrambledand encoded data unit, and transmitting the indication of the scramblingseed and then the scrambled and encoded data unit.

In an implementation form of the third aspect, the method comprises:encoding and/or modulating the indication of the scrambling seedseparately from the at least one data unit.

In a further implementation form of the third aspect, the methodcomprises: including the indication of the scrambling seed in a PHYpreamble.

In a further implementation form of the third aspect, the methodcomprises: including the indication of the scrambling seed in a SIG-Afield or SIG-B field.

In a further implementation form of the third aspect, the methodcomprises: defining the indication of the scrambling seed based onpredetermined bits of one or more signaling fields.

In a further implementation form of the third aspect, the methodcomprises: encoding the indication of the scrambling seed using a BCC.

In a further implementation form of the third aspect, the methodcomprises: encoding the indication of the scrambling seed using a blockcode.

In a further implementation form of the third aspect, the methodcomprises: encoding the indication of the scrambling seed using aHadamard code as a generator matrix.

In a further implementation form of the third aspect, the methodcomprises: modulating the indication of the scrambling seed using BPSK.

With the method of the third aspect, the advantages and effectsdescribed above with respect to the transmitting device of the firstaspect are achieved.

A fourth aspect of the invention provides a method for supporting HARQ,the method comprising: receiving an indication of a scrambling seed andthen at least one scrambled and encoded data unit that is separate fromthe indication of the scrambling seed, descrambling the scrambled andencoded data unit based on the scrambling seed determined from theindication of the scrambling seed, and decoding the encoded data unitusing FEC decoding.

In an implementation form of the fourth aspect, the method comprises:sending to the transmitting device an Acknowledge (ACK) and/or a NotAcknowledge (NACK) message, regarding at least one data unit that wascorrectly and/or incorrectly decoded, receiving, if decoding of at leastone data unit failed, a further indication of a scrambling seed and thena scrambled and encoded retransmission of the failed data unit that isseparate from the further indication of the scrambling seed,descrambling the scrambled and encoded retransmission of the failed dataunit based on a scrambling seed determined from the further indicationof the scrambling seed, decoding the encoded retransmission of thefailed data unit using FEC decoding, and soft combining theretransmission of the failed data unit with the previously receivedfailed data unit.

In a further implementation form of the fourth aspect, the methodcomprises: decoding and/or demodulating a received indication of ascrambling seed separately from a received scrambled and encoded dataunit.

In a further implementation form of the fourth aspect, the methodcomprises: deriving an indication of a scrambling seed frompredetermined bits of one or more received signaling fields.

In a further implementation form of the fourth aspect, the methodcomprises: extracting an indication of a scrambling seed from a PHYpreamble, particularly from a received SIG-A field or SIG-B field.

With the method of the fourth aspect, the advantages and effectsdescribed above with respect to the receiving device of the secondaspect are achieved.

In summary, the embodiments (aspects and implementation forms) of thepresent invention base on performing scrambling after FEC encoding, andperforming descrambling before FEC decoding. As a result:

-   -   The scrambling seed can be changed upon every (HARQ)        retransmission—and LLRs after descrambling can be combined—for        better detection.    -   The scrambling seed is separated from the data unit(s) to make        it more robust.    -   The data unit(s) do not need to be aligned with a scrambling        sequence periodicity (in HARQ mode), and can still be aligned        with a FEC block length.    -   If the scrambling seed would not be separated, then in case of        retransmission of non-first data units (becoming first), the        scrambling seed would have to be included with a first        retransmitted data unit, hence changing coded bits.

It has to be noted that all devices, elements, units and means describedin the present application could be implemented in the software orhardware elements or any kind of combination thereof. All steps whichare performed by the various entities described in the presentapplication as well as the functionalities described to be performed bythe various entities are intended to mean that the respective entity isadapted to or configured to perform the respective steps andfunctionalities. Even if, in the following description of specificembodiments, a specific functionality or step to be performed byexternal entities is not reflected in the description of a specificdetailed element of that entity which performs that specific step orfunctionality, it should be clear for a skilled person that thesemethods and functionalities can be implemented in respective software orhardware elements, or any kind of combination thereof.

BRIEF DESCRIPTION OF DRAWINGS

The above described aspects and implementation forms of the presentinvention will be explained in the following description of specificembodiments in relation to the enclosed drawings, in which

FIG. 1 shows a transmitting device according to an embodiment of theinvention.

FIG. 2 shows a method according to an embodiment of the invention.

FIG. 3 shows a receiving device according to an embodiment of theinvention.

FIG. 4 shows a method according to an embodiment of the invention.

FIG. 5 shows a generator matrix.

FIG. 6 shows a parity check matrix.

FIG. 7 shows a block diagram of a conventional 802.11n transmitter.

FIG. 8 shows a block diagram of a conventional 802.11ax transmitter.

FIG. 9 shows a SERVICE filed.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 1 shows a transmitting device 100 according to an embodiment of theinvention. The transmitting device 100 is configured to support HARQ,particularly HARQ for IEEE 802.11/Wi-Fi. That means, the device 100 maybe an 802.11-standard transmitting device supporting HARQ.

The transmitting device 100 is configured to encode at least one dataunit 101 using FEC coding 102, in order to obtain at least one encodeddata unit 103. The FEC coding 102 may be carried out by a conventionalFEC encoder, as e.g. in the conventional transmitter shown in FIG. 7.The data unit 101 may be a MPDU, and if more than one data unit 101 isencoded, the data units 101 may be in an A-MPDU, i.e. may form a PPDU.

Further, the transmitting device 100 is configured to scramble theencoded data unit 103 based on a scrambling seed 104, in order to obtainat least one scrambled and encoded data unit 106. The scrambling may becarried out by a scrambler, which is accordingly located in the device100 after a FEC encoder that carries out the FEC encoding 102. Thescrambling seed 104 may include a sequence of bits used as input to thescrambler for scrambling the bits of the encoded data unit 103.

The transmitting device 100 is then configured to provide an indication105 of the scrambling seed 104 that is separate from the scrambled andencoded data unit 106. The indication 105 may be designed such that thescrambling seed 104 can be obtained based on it, e.g. can be calculatedor derived from the indication 105.

Finally, the transmitting device 100 is configured to transmit theindication 105 of the scrambling seed 104, and then, i.e. aftertransmitting the indication, transmit the scrambled and encoded dataunit 106 to a receiving device 300, either directly or indirectly.

FIG. 2 shows a corresponding method 200 according to an embodiment ofthe invention, which method 200 can accordingly be carried out by thetransmitting device 100 of FIG. 1. The method 200 is for supportingHARQ, particularly for Wi-Fi.

The method 200 comprises: a step 201 of encoding at least one data unit101 using FEC coding 102; a step 202 of scrambling the encoded data unit103 based on a scrambling seed 104; a step 203 of providing anindication 105 of the scrambling seed 104 that is separate from thescrambled and encoded data unit 106; and a step 204 of transmitting theindication 105 of the scrambling seed 104, and then the scrambled andencoded data unit 106.

FIG. 3 shows a receiving device 300 according to an embodiment of theinvention. The receiving device 300 is configured to support HARQ,particularly HARQ for IEEE 802.11/Wi-Fi, i.e. the device 300 may be an802.11-standard receiving device supporting HARQ.

The receiving device 300 is configured to receive, from a transmittingdevice 100, an indication 105 of a scrambling seed 104, and then, i.e.after receiving the indication 105, to receive at least one scrambledand encoded data unit 106 that is separate from the indication 105 ofthe scrambling seed 104. The transmitting device 100 is particularly theone shown in FIG. 1.

The receiving device 300 is further configured to descramble thescrambled and encoded data unit 106 based on the scrambling seed 104determined from the indication 105 of the scrambling seed 104, in orderto obtain at least one encoded data unit 103. The descrambling may beperformed by a descrambler, as e.g. one as provided in a conventionalreceiver.

Further, the receiving device 300 is then configured to decode theencoded data unit 103 using FEC decoding 301, in order to obtain atleast one data unit 101. The data unit 101 may again be an MPDU, moredata units 101 may be an A-MPDU or PPDU. The FEC decoding 301 may beperformed by a conventional FEC decoder, which is arranged after thedescrambler that carries out the descrambling.

FIG. 4 shows a corresponding method 400 according to an embodiment ofthe invention, which method 400 can accordingly be carried out by thereceiving device 300 of FIG. 3. The method 400 is for supporting HARQ,particularly for WIFI.

The method 400 comprises: a step 401 of receiving an indication 105 of ascrambling seed 104 and then at least one scrambled and encoded dataunit 106 that is separate from the indication 105 of the scrambling seed104; a step 402 of descrambling 402 the scrambled and encoded data unit106 based on the scrambling seed 104 determined from the indication 105of the scrambling seed 104; a step 403 of decoding the encoded data unit103 using FEC decoding 301.

In the following, more details regarding the above-described devices 100and 300, and respectively corresponding to the methods 200 and 400, areprovided. In particular, different solutions are presented for achievingthe two main aspects of embodiments of the invention, namely:

Firstly, a switching of the location/order of the FEC encoding 102 (FECencoder) and scrambling (scrambler) in the transmitting device100—compared to the conventional transmitter—i.e. the scrambler islocated after the FEC encoder to operate on the encoded bits of the dataunit 101. And likewise, a switching of the location/order of thedescrambling (descrambler) and FEC decoding 301 (FEC decoder) in thereceiving device 300—compared to the conventional receiver—i.e. thedescrambler is located before the FEC decoder, so that the descrambleroperates on the encoded bits of the data unit 101.

Secondly, a separation of the indication 105 of the scrambling seed 104,e.g. the SERVICE field that is used conventionally, from the dataunit(s) 101. That is, the indication 105 is either provided in adifferent part of a transmission than the data unit(s) 101, or isencoded and/or modulated differently than the data unit(s).

Since preferably the scrambling seed 104 changes at every(re)transmission, while still sending the same codeword (up toredundancy versions), the scrambling in the transmitting device 100operates on the coded bits of the data unit 101. This allows the LLRs(soft-bits) at the receiving device 300 to be descrambled prior tocombining. This is true for both BCC and LDPC. Thus, the indication 105of the scrambling seed 104 (e.g. the SERVICE field) is providedseparately from the data unit 101. The transmitting device 100 indicates105 the scrambling seed 104 to the receiving device 300 before dataunit(s).

A first option for indicating the scrambling seed 104 is now described.In particular, a very simple solution is to remove the indication 105(e.g. the entire SERVICE field) from its current location (before thedata portion), and move the scrambling seed indication 105 to the PHYpreamble. That is, the transmitting device 100 may be configured toinclude the indication 105 of the scrambling seed 104 in a PHY preamble,and accordingly the receiving device 300 may be configured to extractthe indication 105 of the scrambling seed 104 from the PHY preamble. ThePHY preamble is a different part of a transmission than the data portion(data unit(s)).

For example, the scrambling seed (which may be 7 bits) may be indicated105 within SIG-A (for all STAs) or within SIG-B (for each STA). Thatmeans, the transmitting device 100 may be configured to include theindication 105 of the scrambling seed 104 in a SIG-A field or SIG-Bfield, and accordingly the receiving device 300 may be configured toextract the indication 105 of the scrambling seed 104 from the SIG-Afield or SIG-B field received from the transmitting device 100. This isa simple solution, but a bit overhead is required.

Alternatively, an existing field may be used (e.g. some combination ofthe bits representing the STA's STA-ID & SIG-B Cyclic Redundancy Check(CRC) combination of STA's STA-ID and L-SIG length, 7 Least SignificantBits (LSB), of L-SIG length), in order to generate a new, e.g.pseudo-random scrambling seed 104, using e.g. a predefined recipe (thusknown to both transmitting device 100 and receiving device 300). Thatis, the transmitting device 100 may be configured to define theindication 105 of the scrambling seed 104 based on predetermined bits ofone or more signaling fields, and the receiving device 300 mayaccordingly be configured to derive the indication 105 of the scramblingseed 104 from predetermined bits of one or more signaling fieldsreceived from the transmitting device 100.

A second option for indicating the scrambling seed 104 is now described.In particular, the indication 105 (e.g. SERVICE field) may be maintainedas it is and at the location it is conventionally, but may be encodedand/or modulated separately from the data unit(s) 101 in thetransmitting device 100, so that the receiving device 300 can decodeand/or demodulate it separately from the data unit(s), can obtain thedescrambling seed 104, and can use it immediately on the LLRs.

BCC encoding can, for instance, be used. If BCC (and hence Viterbidecoding) is used, appending the indication 105 (e.g. SERVICE field, orseed information) may be necessary to ensure the Viterbi decoder hasenough depth.

A third option for indicating the scrambling seed 104 is now described.In particular, the indication 105 (e.g. SERVICE field) may be maintainedas it is and at the location it is conventionally, but may be encodedand/or modulated separately from the data unit(s) 101. For instance, inorder to ensure maximum robustness, BPSK modulation with some block-codeencoding, for example of rate 1/2, may be used, regardless of theModulation and Coding Scheme (MCS) used for the data unit(s) 101. Hence,the indication 105 (SERVICE field) is always encoded and modulated usinga very robust scheme.

This means that the number of tones allocated for the indication 105(e.g. SERVICE field) is always fixed, hence it is easy to compute thenumber of tones required for the data unit(s) 101, LDPC parameters(shortening/puncturing/repetition), pre-FEC bits, etc. A simple blockcode can be used. For example, one can use a systematic linear blockcode with coding rate 1/2, where the scrambling seed 104 is appendedwith 1 bit (to make it 8 bits), and a Hadamard code may be used for thegenerator matrix 500, which is shown in FIG. 5. A parity check matrix isshown in FIG. 7.

The present invention has been described in conjunction with variousembodiments as examples as well as implementations. However, othervariations can be understood and effected by those persons skilled inthe art and practicing the claimed invention, from the studies of thedrawings, this disclosure and the independent claims. In the claims aswell as in the description the word “comprising” does not exclude otherelements or steps and the indefinite article “a” or “an” does notexclude a plurality. A single element or other unit may fulfill thefunctions of several entities or items recited in the claims. The merefact that certain measures are recited in the mutual different dependentclaims does not indicate that a combination of these measures cannot beused in an advantageous implementation.

What is claimed is:
 1. Transmitting device (100) for supporting HybridAutomatic Repeat Request, HARQ, the transmitting device (100) beingconfigured to: encode at least one data unit (101) using Forward ErrorCorrection, FEC, coding (102), scramble the encoded data unit (103)based on a scrambling seed (104), provide an indication (105) of thescrambling seed (104) that is separate from the scrambled and encodeddata unit (106), and transmit the indication (105) of the scramblingseed (104) and then the scrambled and encoded data unit (106) to areceiving device (300).
 2. Transmitting device (100) according to claim1, configured to: encode and/or modulate the indication (105) of thescrambling seed (104) separately from the at least one data unit (101).3. Transmitting device (100) according to claim 1, configured to:include the indication (105) of the scrambling seed (104) in a physicallayer, PHY, preamble.
 4. Transmitting device (100) according to claim 1,configured to: include the indication (105) of the scrambling seed (104)in a Signal A, SIG-A, field or Signal B, SIG-B, field.
 5. Transmittingdevice (100) according to claim 1, configured to: define the indication(105) of the scrambling seed (104) based on predetermined bits of one ormore signaling fields.
 6. Transmitting device (100) according to claim1, configured to: encode the indication (105) of the scrambling seed(104) using a Binary Convolution Code, BCC.
 7. Transmitting device (100)according to claim 1, configured to: encode the indication (105) of thescrambling seed (104) using a block code.
 8. Transmitting device (100)according to claim 7, configured to: encode the indication (105) of thescrambling seed (104) using a Hadamard code as a generator matrix (500).9. Transmitting device (100) according to claim 1, configured tomodulate the indication (105) of the scrambling seed (104) using BinaryPhase Shift Keying, BPSK.
 10. Receiving device (300) for supportingHybrid Automatic Repeat Request, HARQ, the receiving device (300) beingconfigured to: receive from a transmitting device (100) an indication(105) of a scrambling seed (104) and then at least one scrambled andencoded data unit (106) that is separate from the indication (105) ofthe scrambling seed (104), descramble the scrambled and encoded dataunit (106) based on the scrambling seed (104) determined from theindication (105) of the scrambling seed (104), and decode the encodeddata unit (103) using Forward Error Correction, FEC, decoding (301). 11.Receiving device (300) according to claim 10, configured to: send to thetransmitting device (100) an Acknowledge, ACK, and/or a Not Acknowledge,NACK, message, regarding at least one data unit (101) that was correctlyand/or incorrectly decoded, receive from the transmitting device (100),if decoding of at least one data unit (101) failed, a further indication(105) of a scrambling seed (104) and then a scrambled and encodedretransmission of the failed data unit (101) that is separate from thefurther indication (105) of the scrambling seed (104), descramble thescrambled and encoded retransmission of the failed data unit (101) basedon a scrambling seed (104) determined from the further indication (105)of the scrambling seed (104), decode the encoded retransmission of thefailed data unit using Forward Error Correction, FEC, decoding, (301)and soft combine the retransmission of the failed data unit (101) withthe previously received failed data unit (101).
 12. Receiving device(300) according to claim 10, configured to: decode and/or demodulate areceived indication (105) of a scrambling seed (104) separately from areceived scrambled and encoded data unit (106).
 13. Receiving device(300) according to claim 10, configured to: derive an indication (105)of a scrambling seed (104) from predetermined bits of one or moresignaling fields received from the transmitting device (100). 14.Receiving device (300) according to claim 10, configured to: extract anindication (105) of a scrambling seed (104) from a physical layer, PHY,preamble, particularly from a Signal A, SIG-A, field or Signal B, SIG-B,field, received from the transmitting device (100).
 15. Method (200) forsupporting Hybrid Automatic Repeat Request, HARQ, the method comprising:encoding (201) at least one data unit (101) using Forward ErrorCorrection, FEC, coding (102), scrambling (202) the encoded data unit(103) based on a scrambling seed (104), providing (203) an indication(105) of the scrambling seed (104) that is separate from the scrambledand encoded data unit (106), and transmitting (204) the indication (105)of the scrambling seed (104) and then the scrambled and encoded dataunit (106).
 16. Transmitting method (200) according to claim 15,comprising: encoding and/or modulating the indication (105) of thescrambling seed (104) separately from the at least one data unit (101).17. Transmitting method (200) according to claim 15, comprising:including the indication (105) of the scrambling seed (104) in aphysical layer, PHY, preamble, particularly in a Signal A, SIG-A, fieldor Signal B, SIG-B, field.
 18. Transmitting method (200) according toclaim 15, comprising: defining the indication (105) of the scramblingseed (104) based on predetermined bits of one or more signaling fields.19. Transmitting method (200) according to claim 15, comprising:encoding the indication (105) of the scrambling seed (104) using aBinary Convolution Code, BCC.
 20. Transmitting method (200) according toclaim 15, comprising: encoding the indication (105) of the scramblingseed (104) using a block code.